1. Field of the Invention
The present invention relates to a modified radial motion method for modifying lengthwise curvature of face-milling spiral bevel and hypoid gears, which is capable of modifying a locus of a cutter center into a curve, without changing a head cutter's geometry, by providing modified radial motion of the head cutter cooperating with rotation of a cradle.
2. Description of the Prior Arts
The purpose of lengthwise curvature modification is to change the contact pattern of the gear sets. The related existing methods are:
1) Changing the head cutter's geometry. Such as U.S. Pat. No. 5,004,127 proposes method to modify tooth form with modified grinding wheel.
2) Modifying the roll ratio between the cradle and the work-gear. Just as disclosed by U.S. Pat. No. 4,780,990.
However, adjustability of the gear set (V-H value) is accordingly changed after the lengthwise curvature modification in tooth surface. The main problem that the industrial sector confronts is the adjustability of the gear set decreases while the tooth contact pattern is increasing (decrease the Heizian contact stress). Adjustability of the gear set and tooth contact are the main index data indicating the quality of the gear, which usually contradict to each other. The primary object of the present invention is to solve the contradiction.
In recent years, CNC hypoid generator has taken the place of the conventional cradle type hypoid generator. The motion of CNC hypoid generator is holding-type-orthogonal motion. U.S. Pat. No. 4,981,402 discloses a Multi-axis bevel and hypoid gear generating machine having six flexibilities, which including three translational axes (x-axis, y-axis, z-axis) and three rotational axes (cutter-axis, work-gear-axis and machine-root-angle-axis). The three translational axes are arranged in mutually orthogonal directions. The spatial relationship between the cutter-axis and the work-gear-axis is described by the machine-root-angle-axis and the three translational axes (x-axis, y-axis, z-axis). Another hypoid generating machine disclosed by WIPO 02/066,193, which has six flexibilities, including three translational axes (x-axis, y-axis, z-axis) and three rotational axis (cutter-axis, work-gear-axis and machine-root-angle-axis). The three translational axes are arranged in mutually orthogonal directions. The spatial relationship between the cutter-axis and the work-gear-axis is described by the machine-root-angle-axis and the three translational axes (x-axis, y-axis, z-axis). The machine-root axis consists of cradle.
There are two lengthwise curvature modification methods existing in the industrial sector, one is head cutter's geometry change and the other is by modifying the roll ratio between the cradle and the work-gear. However, the head cutter's geometry change requires the resetting of the machine setting, which is time consuming. The cradle type hypoid generating machine being currently applied in the industrial sector is shown in FIG. 1, wherein cutter 1 is mounted on a rotation plate 2, on the cutter 1 is arranged with blade. The rotation plate 2 is mounted on an eccentric disc 3, the tilt of the head cutter is determined by rotation angles of i (rotation plate 2) and j (eccentric disc 3). The eccentric disc 3 is disposed on the cradle 5. When the head cutter is not tilt, i=0,j=0, cutter 1 is mounted on the cradle 5 directly. The radial setting SR is the shortest distance between cutter-axis b—b and cradle-axis a—a on the reference machine plane. The machine plane is fixed to the basement and the unit normal is the cradle-axis a—a. When the cradle rotates, the generating of tooth is achieved by taking use of the relative motion between the cutter and the work gear 4. The radial setting of the cradle type hypoid generating machined currently used in industrial sector is constant, in case of rotation of the cradle, the locus of the cutter center on the machine plane is a circular arc, rotation angle of the cradle q and the radial setting SR determine the position of the cutter center.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages of the conventional lengthwise curvature modification methods.